The present invention relates to a scanning probe microscope which may detect a physical quantity with a high resolution, in which an anti-vibration table is added to a scanning probe microscope such as an atomic force microscope or a magnetic microscope for detecting a physical quantity such as an atomic force received from a sample even if the system is provided in a noisy space such as a clean room or the like for semiconductor manufacture.
The atomic force microscope which is a kind of a scanning probe microscope has been researched as a surface shape observation means for a novel insulative substance since it was invented by G. Binnig who was the inventor of an STM (Physical Review Letters vol. 56, p930, 1986). In principle, the atomic force that acts between the sample and a detecting chip whose tip end is sufficiently sharpened is measured as a deviation of a spring element on which the detecting chip is mounted, the surface of the sample is scanned while keeping constant the deviation quantity of the spring element, and the shape of the surface of the sample is measured as shape information as a control signal for keeping constant the deviation quantity of the spring element.
The spring element deviation detecting means is usually divided into an optical system and an STM system using a tunnel current.
The STM system utilizes a so-called tunnel phenomenon in which a current starts to flow when a voltage is applied to two conductors when the latter are caused to be close to each other by a distance of several nano meters to several angstroms. The conductivity is applied to the spring element. The sharp metal needle is located close to the spring element within about one nano meter. The tunnel current is caused to flow therethrough. Its current value is controlled as a shift signal of the spring element.
It is also reported that an optical system such as an example using an interfering method (Journal of Vacuum Science Technology A6(2), p266, March/April 1988) or an example referred to as an optical lever system in which a laser beam is applied to the spring element and a deviation of a reflective light therefrom is detected by an optical detecting element as the shift signal (Journal of Applied Physics 65(1), 1 p164, January 1989) is used.
If the scanning probe microscope is one in which the probe disposed in a position facing the sample is to receive an atomic force from the sample, then it is called an atomic force microscope. If it receives a magnetic force, it is called a magnetic force microscope. Thus, it is referred to as one that may detect a state of the sample by detecting the various forces generated from the sample.
The scanning probe microscope is provided with a very high sensitivity detecting portion such that a difference in shape or the like between atoms may be identified. On the other hand, since the scanning probe microscope is provided with the high sensitivity detecting portion, the probe microscope is also sensitive to vibration or sound from the outside. Namely, if the sample and the detecting portion are changed (vibrated) relative to each other by the vibration or sound from the outside, then the variation component is also detected. Therefore, the variation component by the vibration from the outside is detected by the detecting portion whereby it is mixed with the signal component representative of the sample condition. As a result, the resolution of the scanning probe microscope is degraded. For this reason, in order to avoid the adverse affect of the vibration, in general, the scanning probe microscope is designed to be small in size and high in rigidity.
However, there is another demand for measuring any desired position on an eight inch wafer of the type supplied recently to a semiconductor manufacture system and there is provided a scanning probe microscope (large size stage-type probe microscope) into which a large size stage is installed. However, if the scanning probe microscope becomes large in size, it is rather difficult to avoid the adverse affect of the vibration from the installation site. Incidentally, the large size scanning probe microscope is disclosed in detail in the literature (J. Vac. Sci. Technol. B 12(3), May/June 1994 P1572).
The vibration of the floor on which the scanning probe microscope is provided constitutes the main vibration from the outside. A variety of frequency components are present depending upon the installation circumstances in the floor vibration. There is a vibration having a low frequency component like several Hz (10 Hz or less). In general, in the element part such as the detecting portion or the like of the scanning probe microscope, an anti-vibration table is provided for reducing the adverse affect of the vibration from the floor and the detecting portion is structured on the base of the anti-vibration table. In general, it is known to use pneumatic means as the anti-vibration table. However, since a pneumatic spring mechanism is basically a spring element, it has a resonance point. Usually, the resonance point is low in the range of about 1 to 3 Hz. In such an anti-vibration table having a low resonance point, it is impossible to reduce the vibration component for the vibration having a low frequency such as the vibration component of the floor, typically 4 Hz or less. Inversely, this is amplified on the anti-vibration table. On the other hand, since clean conditions are needed in the semiconductor manufacture system, mass-production has been developed in a so-called clean room. However, since the clean room must have a clean air space, clean air is circulated through the clean room, and also many devices including evaluation devices are provided in the room, and consequently various noises are generated. Also, the building itself which is furnished with the clean room exhibits a vibration component. For this reason, there exists a vibration having a high frequency or a vibration of low frequency vibration on the floor within the clean room.
An object of the present invention is to provide a scanning probe microscope in which a novel vibration base for the probe microscope is provided for forcibly reducing an affect of vibrations in a range from a high frequency to a low frequency not only for high frequency components caused by a sound or the like but also for low frequency components caused by an apparatus installation site such as a clean room or the like which produces a low frequency component with a rather high intensity, thereby eliminating a degradation of the inherent resolution possessed by the probe microscope.